Nanotechnology has been used in the biomedical fields. Specifically, single-walled carbon nanotubes (SWNTs) have been applied in various biological systems. One intrinsic property of SWNTs is their ability to cross cellular membranes without eliciting cytotoxicity. Another intrinsic property of SWNTs is their strong optical absorbance in the near-infrared (NIR) region. It was reported that SWNTs could enhance thermal destruction of cells during NIR laser irradiation and radiofrequency irradiation. Since biological tissues are relatively transparent to light in the range of 700-1100 nm, the ideal SWNT for photothermal therapy should have an absorption band in the NIR region. Furthermore, it is desirable to have nanotubes with uniform size so that a narrow absorption peak can be used for effective optical irradiation. The CoMoCAT method, discussed in “Controlled production of single-wall carbon nanotubes by catalytic decomposition of CO on bimetallic Co—Mo catalysts” by Kitiyanan B, Alvarez W E, Harwell J H, Resasco D E (2000) in Chem. Phys. Lett. 317:497-503, incorporated herein by reference, produces SWNTs with a narrow and intense absorption band around 980 nm.
For biological applications, SWNTs should be prepared in aqueous suspension; surfactants are needed for stable dispersion to avoid aggregation of nanotubes. Sodium dodecylbenzene sulfonate (NaDDBS), sodium carboxymethylcellulose (NaCMC), and sodium cholate (NaCholate) are commonly used as surfactants for nanotubes.
The electronic structure of SWNTs is sensitive to changes in the surrounding electrostatic environment. For example, their optical response can be greatly changed by surface charge transfers or by adsorption of molecules. Therefore, it is crucial to have a SWNT solution with appropriate optical properties for biomedical applications.
Photothermal therapy can be effective for local cancer treatment due to the sensitivity of tumor cells to temperature elevation. Laser immunotherapy was developed to combine photothermal reaction with immunological stimulation to treat metastatic tumors. Its selective photothermal effect serves as the first line of assault on the tumor, using a combination of an NIR laser irradiation and a light-absorbing dye. An immunological stimulant is used concurrently to induce immunological responses. A new compound, glycated chitosan (GC), was developed as such an immunostimulant. Laser immunotherapy using GC and the light-absorbing dye has been proven to be highly effective in the treatment of metastatic tumors in pre-clinical studies. This method has also been used to treat late-stage breast cancer patients with promising outcomes.